The present invention relates generally to sending data by electromagnetic (EM) waves and in particular, to sending data through polarization modulation of electromagnetic waves.
The rise in use of the EM-spectrum has created a great demand to use that limited spectrum more efficiently, and with enhanced security. Advances in data processing and information theory help, but there is room for improvement on the hardware side. Amplitude modulation (AM) uses a low frequency data signal, such as a human voice, to modulate the amplitude a much higher constant frequency carrier signal to form the radiated EM transmission wave. Alternatively, frequency modulation (FM) uses the low frequency data to modulate the frequency of a much higher frequency carrier signal of constant amplitude to form the radiated EM transmission wave.
While most modern radios make use of both in phase (I) and quadrature (Q) signals, i.e. two independent data streams, they do not take advantage of the additional throughput offered by using multiple polarizations. This is because often the orientation of the receive antenna is not known and thus signals are sent with a single polarization (either circular or linear).
Polarization is a property of some radiated EM waves. Polarization examples include linear or plane, elliptical, and circular. Polarization of transmitted signals is used to enhance transmission characteristics of radio waves, i.e. by polarizing a radiated EM wave to match the orientation of a receiving antenna (hereinafter alternatively referred to as receive antenna or receiver). Because the orientation of the receiver is unknown, sending data from a sending antenna (hereinafter alternatively referred to as radiating antenna or radiator or transmitter) in a circular polarization either clockwise (CW) or counterclockwise (CCW) is more effective than linear polarizations because the receiver can rotate in the x-y plane without effect on the signals and the degradation due to the receiver being off axis to the z-axis is similar to that of linear polarizations.
Polarization multiplexing is used in the optical regime where two different light beams, one with CW circular polarization and another with CCW circular polarization are combined and sent over an optical fiber transmission line at the same time to double the available signal bandwidth. This is possible because the orientation of the optical receiver is known in comparison to the fiber orientation so that the two differently polarized optical signals can be separated and each treated individually as separate signal transmission paths. In most cases antennas are single-port antennas capable of transmitting or receiving only a specific type of polarization.